The present invention relates to lipophilic diesters of a chelating agent, to processes of synthesizing these agents, to pharmaceutical compositions thereof and to their use in treating a condition or disease related to abnormal levels of divalent metal ions, in particular to elevated levels of intracellular calcium ions. More particularly the invention relates to diesters of 1,2-bis(2 aminophenoxy)ethane-N,N,Nxe2x80x2,Nxe2x80x2-tetraacetic acid denoted herein as BAPTA which are stable lipophilic derivatives of divalent metal ions chelator.
Metal ions such as calcium, manganese, magnesium, copper, zinc and ferrous ions play a pivotal role in biological systems by regulating protein structure, enzyme activity and cellular signaling. Various diseases or pathological states including brain and cardiac ischemia, stroke, myocardial infarction, epilepsy, chronic neurodegenerative diseases such as Alzheimer""s disease, Parkinson""s disease and acute inflammation are all believed to be related to the phenomenon of abnormally elevated intracellular calcium levels. Other diseases associated with neuronal and muscular hyperactivity such as urinary incontinence, prostatic hypertrophy, muscular spasm, arterial hypertension, asthma, irritable bowel syndrome, have all been related to elevated levels of intracellular divalent ions such as calcium and zinc.
Intracellular calcium is an important determinant for cell death, irrespective of the initial insult sustained by the cell. It may be involved in cell death in lymphocyte and killer cell mediated damage of target cells, in organ damage during transplantation, and in other types of tissue damage including ischemic insults. Calcium channel blockers or cell membrane permeable forms of calcium chelators have been suggested to protect against tissue injury or to decrease tissue damage.
The cell damage occurring in ischernia may be secondary to the influx and/or intracellular release of Ca2+ ions (Choi, Trends Neurosci., 1988, 11, 465-469; Siesjo and Smith, Arzneinittelforschung, 1991, 41, 288-292). Similarly, calcium influx appears to play an important role in the genesis of epileptic seizures. Although a significant portion of intracellular calcium arrives from intracellular stores, current research suggests that calcium entry blockers may have anticonvulsant activity (see e.g. Meyer, 1989, Brain Res. Rev 14, 227-243).
Accordingly, certain pharmacological strategies have been developed intending to prevent or treat this pathological accumulation of intracellular calcium, which may result from pathological release of calcium from intracellular deposits or by detrimental calcium influx into cells.
Drugs which are currently or potentially useful for treatment of calcium associated disorders include: (i) calcium channel blockers, (ii) drugs affecting calcium balance by modification of intracellular calcium storage sites, and (iii) intracellular calcium chelating agents. Calcium channel blockers used in clinical practice are represented by Verapamil, Nifedipine and Diltiazem. The major toxicities associated with the use of such compounds involve excessive vasodilation, negative inotropy, depression of the sinus nodal rate, and A-V nodal conduction disturbances. Drugs affecting calcium mobilization and/or sequestration, like calcium channel blockers, exhibit rather narrow specificity.
Among the highest affinity and most selective calcium chelators are various derivatives of 1,2-bis-(2-aminophenoxyethane)-N,N,Nxe2x80x2,Nxe2x80x2,-tetraacetic acid (BAPTA) which was originally described by Tsien (Biochem. 19, 2396, 1980). Various fluorescent and other reactive derivatives of BAPTA have been disclosed for example in U.S. Pat. Nos. 4,603,209, 4,849,362, 5,049,673 and 5,453,517. None of these disclosed derivatives is a stable diester of the chelator.
The use of calcium chelators for reducing injury to mammalian cells is disclosed in the International Publication No. WO 94/08573, which describes use of cell membrane permeable esters of calcium chelating agents as prodrugs for clinical requirements. Available cell membrane permeable chelators of Ca++ and other divalent metal ions, include acetoxymethyl esters such as ethyleneglycol bis 2-aminoethyl ether N,N,Nxe2x80x2,Nxe2x80x2,tetra-acetic acid acetoxymethyl ester (EGTA-AM), ethylene diamine tetra-acetic acid acetoxymethyl ester (EDTA-AM) and 1,2-bis(2-aminophenoxy)ethane-N,N,Nxe2x80x2,Nxe2x80x2-tetra-acetic acid acetoxymethyl ester (BAPTA-AM). These known complex molecules are prodrugs digested by ubiquitous esterases, consequently causing activation of the chelator in the intracellular space. Thus, the esterase-sensitivity of these compounds leads, under physiological conditions, to high circulating levels of free BAPTA and low efficacy of the drug at the target site. Accordingly, BAPTA-AM, for example, has to be used at relatively high therapeutic dosage that is associated with toxicity.
In accordance with one aspect of the present invention, there are provided novel stable lipophilic diesters of chelating agents. Thus, the invention provides a stable di-esterified carboxylic acid (a) with hydroxy compound (b), where (a) is a pharmaceutically acceptable chelating agent for divalent metal ions having the formula (HOOCxe2x80x94CH2xe2x80x94)2xe2x80x94Nxe2x80x94Axe2x80x94Nxe2x80x94(xe2x80x94CH2COOH)2 wherein A is saturated or unsaturated, aliphatic, aromatic or heterocyclic linking radical containing, in a direct chain link between the two depicted nitrogen atoms, 2-8 carbon atoms in a continuous chain which may be interrupted by 2-4 oxygen atoms, provided that the chain members directly connected to the two depicted nitrogen atoms are not oxygen atoms, and (b) is a pharmaceutically acceptable alcohol selected from the group of straight chain or branched, saturated or unsaturated alkyl, aminoalkyl and substituted or unsubstituted arylalkyl radicals; and pharmaceutically acceptable salts of said di-esterified carboxylic acids.
According to preferred embodiments of the present invention there are provided diesters of the chelating agents ethylene-1,2-diamine-N,N,Nxe2x80x2,Nxe2x80x2,-tetraacetic acid, ethylene-1,2-diol-bis-(2-aminoethyl ether)-N,N,Nxe2x80x2,Nxe2x80x2-tetraacetic acid and in particular diesters of 1,2-bis-(2-aminophenoxy)ethane-N,N,Nxe2x80x2,Nxe2x80x2-tetraacetic acid.
According to a more preferred embodiment of the invention, there are provided diesters of the general formula I: 
wherein the substituents on the aromatic rings are in the ortho position;
R is selected from the group consisting of CnH2n+1(n=1-10), CnH2n+1(OCH2CH2)m(n=1-20, m=1-6), (CnH2n+1)2N(CH2)m(n=1-6, m=1-6) and substituted or unsubstituted ArCH2; and M denotes any physiologically acceptable cation.
Currently preferred compounds according to the invention are compounds of the general formula I wherein R is selected from the group consisting of: C2H5, C3H7, i-C3H7, C4H9, C7H15, C8H17, CH2C6H5, CH3OCH2CH2, C2H5OCH2CH2, C3H7OCH2CH2, C4H9OCH2CH2, C7H15OCH2CH2, C8H17OCH2CH2, C10H21OCH2CH2, C16H33OCH2CH2, C18H37OCH2CH2, CH3(OCH2CH2)2, C2H5(OCH2CH2)2, C4H9(OCH2CH2)2, C6H13(OCH2CH2)2, C7H15(OCH2CH2)2, C8H17(OCH2CH2)2, C10H21(OCH2CH2)2, CH3(OCH2CH2)3, (CH3)2NCH2CH2, C7H15(OCH2CH2)3.
More preferred are compounds of the general formula I wherein R is selected from the group consisting of: C2H5, C3H7, C4H9, C7H15, C8H17, C8H17OCH2CH2, C10H21OCH2CH2, C16H33OCH2CH2, C18H37OCH2CH2, C8H17(OCH2CH2)2, C10H21(OCH2CH2)2.
For certain pharmaceutical embodiments according to the present invention, most preferred are compounds of the above-depicted general formula I wherein R is C8H17or C8H17OCH2CH2.
In accordance with another aspect of the invention, there are provided pharmaceutical compositions comprising as an active ingredient a stable lipophilic diester of a chelating agent according to the invention and a pharmaceutically acceptable diluent or carrier. The pharmaceutical compositions may be in liquid or solid dosage forms and may be orally, parenterally or intranasally administered.
The lipophilic diesters of chelating agents according to the invention are useful in the treatment or prevention of metal ion-associated disorders, for example, disorders associated with abnormal levels of manganese, magnesium, copper, zinc, iron, cadmium, mercury, cobalt, and in particular calcium ions. Thus, in yet another aspect, the present invention provides a method for treating a disease or disorder related to an excess of divalent metal ions, comprising administering to an individual in need thereof a therapeutically effective amount of a stable lipophilic diester of a pharmaceutically acceptable chelating agent for divalent metal ions. In particular, the present invention provides a method for treating a disease or disorder related to an excess of intracellular Ca++ ions, such as brain and cardiac ischemia, stroke, myocardial infarction, epilepsy, Alzheimer""s disease, Parkinson""s disease, acute inflammation, urinary incontinence, prostatic hypertrophy, muscular spasm, arterial hypertension, asthma and irritable bowel syndrome. Said method comprising administering to an individual in need thereof a therapeutically effective amount of a pharmaceutically acceptable diester of a chelating agent in accordance with the invention. The compounds of the invention may also be useful in medical treatments such as open heart surgery.